Seasonal patterns in δ2 H values of multiple tissues from Andean birds provide insights into elevational migration

Geographic variation in the altitudinal migration patterns, body size, oxidative status and exploratory behavior in a neotropical bird

To cope with life in the mountains, populations of the same species can exhibit substantial variability in their altitudinal migration patterns and phenotypes in response to local weather conditions. Studying such variability can provide valuable insights into how local populations respond to environmental challenges, and this information can be useful for conservation efforts in mountain ecosystems. Here, we used δ²H values of feathers and blood to evaluate latitudinal variation in altitudinal migration patterns and its possible links with body size, oxidative status, and exploratory behavior in 72 individuals of rufous‐collared sparrow (Zonotrichia capensis) that breed at low and high elevations in the center (~33°) and south (~38°) of Chile. Our results show that both altitudinal migration patterns and oxidative status were significantly influenced by the latitude of breeding sites, while exploratory behavior was associated with elevation. Notably, we found that fast‐explorer birds inhabiting low elevations in central Chile displayed higher levels of oxidative damage than slow‐explorer birds. These outcomes underscore the possibility of local adaptations in response to diverse local environmental conditions in the Andes. We discuss the implications of latitude, elevation, and environmental temperature in shaping the observed patterns and highlight the significance of identifying local adaptations in mountain birds for better predicting their response to climate change and other challenges stemming from anthropogenic activities.

Life history and ecology might explain incongruent population structure in two co-distributed montane bird species of the Atlantic Forest

Comparative phylogeography is a powerful approach to investigate the role of historical and environmental processes in the evolution of biodiversity within a region. In this regard, comparative studies of species with similar habitat preferences are valuable to reduce the confounding influence of habitat association when interpreting phylogeographic patterns. In the Atlantic Forest of South America, phylogeographic studies of highland and lowland species have shown distinct population structure patterns so far, suggesting that such species have responded differently to Pleistocene glacial cycles. Herein, we performed a comparative analysis using molecular data and paleodistribution models of two Montane Atlantic Forest (MAF) co-distributed passerine birds with similar habitat requirements but with distinct life-history traits and ecologies: the frugivore lek-breeding Blue Manakin (Chiroxiphia caudata) and the insectivore and socially monogamous Drab-Breasted Bamboo Tyrant (Hemitriccus diops). We aimed to shed light on the role of contrasting life histories and ecologies onto the demography and population structure of MAF species. We sampled both species throughout most of their distribution range, sequenced a mitochondrial and a nuclear molecular marker, and used standard phylogeographic methods to investigate population structure and ecological niche modeling (ENM) to infer the species' paleodistributions. Our analyses recovered a phylogeographic break in H. diops in the region of the Doce River, but no genetic structure in C. caudata. We also found higher differentiation among subpopulations within each lineage of H. diops than among subpopulations of C. caudata. We suggest that these discrepancies in population structure might be due to distinct life-history traits and their impact on gene flow and generation time. For example, while H. diops is an insectivore species, C. caudata is a frugivore and the latter ecological aspect likely selects for a higher dispersion distance. Additionally, because C. caudata is a lek-breeding species, it has a longer generation time than H. diops. These traits could hinder genetic differentiation when populations become geographically isolated. Nonetheless, both species showed some common biological features, such as signatures of synchronous population expansion and larger distribution ranges during the Last Glacial Maximum, possibly due to similar cold tolerance.

Stable isotope analysis of multiple tissues from Hawaiian honeycreepers indicates elevational movement

We have limited knowledge of the patterns, causes, and prevalence of elevational migration despite observations of seasonal movements of animals along elevational gradients in montane systems worldwide. While a third of extant Hawaiian landbird species are estimated to be elevational migrants this assumption is based primarily on early naturalist's observations with limited empirical evidence. In this study, we compared stable hydrogen isotopes (δ2H) of metabolically inert (feathers) and active (blood plasma, red blood cells) tissues collected from the same individual to determine if present day populations of Hawaiian honeycreepers undergo elevational movements to track areas of seasonally high flower bloom that constitute significant food resources. We also measured stable carbon isotopes (δ13C) and stable nitrogen isotopes (δ15N) to examine potential changes in diet between time periods. We found that the majority of 'apapane (Himatione sanguinea) and Hawai'i 'amakihi (Chlorodrepanis virens) captured at high elevation, high bloom flowering sites in the fall were not year-round residents at the capture locations, but had molted their feathers at lower elevations presumably in the summer after breeding. δ2H values of feathers for all individuals sampled were higher than blood plasma isotope values after accounting for differences in tissue-specific discrimination. We did not find a difference in the propensity of elevational movement between 'apapane and Hawai'i 'amakihi, even though the 'amakihi is considered more sedentary. However, consistent with a more generalist diet, δ15N values indicated that Hawai'i 'amakihi had a more diverse diet across trophic levels than 'apapane, and a greater reliance on nectar in the fall. We demonstrate that collecting multiple tissue samples, which grow at different rates or time periods, from a single individual can provide insights into elevational movements of Hawaiian honeycreepers over an extended time period.

Importance of suspended particulate organic matter in the diet of Nephrops norvegicus (Linnaeus, 1758)

The extent to which commercially important Nephrops norvegicus lobsters feed on particulates in the wild is unknown, even though this could be an important way for burrow-dwelling females to avoid starvation during the long breeding season. This was investigated using δ¹³C and δ¹⁵N isotopic signatures in tissues with long and short turnover rates to provide diet discrimination and compare this between males and females. Secondary objectives examined size-related differences and calculated the trophic position based on the new results. Almost half the diet (47%) was made up of suspended particulate organic matter (POM_susp) alone. Fish was another important item in the diet, with plankton and invertebrate sources coming much lower down in dietary importance. Significantly more suspension feeding was observed in small or medium sized individuals than large ones in both sexes. However, there were no sex-related patterns, despite females being restricted to burrows for part of the analysis period. Female diet was almost identical to males and POM_susp comprised a large component of the diet in both sexes. The trophic position was estimated at 2.94 ± 0.16 (mean ± SD), which was at the lower end of the range reported in previous studies (2.60 to 4.32).

Intraspecific variation in exploratory behavior and elevational affinity in a widely distributed songbird

Populations of the same species can vary substantially in their behavioral and morphometric traits when they are subject to different environmental pressures, which may lead to the development of different adaptive strategies. We quantified variation in exploratory behavior and morphometric traits among two rufous-collared sparrow populations that occur at low and high elevations in central Chile. Moreover, we used census and δ²H values of feather and blood to evaluate migration. We found that individual sparrows inhabiting high elevations were larger and showed more intense exploratory behavior in comparison with those that were captured at lower elevation. Moreover, we observed a steady decline in sparrow abundance during the winter and similar δ²H values for blood collected in the winter and summer at this site, which were significantly lower than blood δ²H values observed at low elevation. This pattern suggests that individuals do not move long distances during winter, and likely they remain at similar elevations in refuge habitats. As predicted, our results support the existent of different adaptive strategies among populations of the same species, and suggest that the combination of behavioral, morphometric, and stable isotope data is a novel and robust integrative approach to assess differences in adaptation across environmental gradients.